The present invention relates to a single-tube color video camera apparatus having a color separation stripe filter which is positioned in the light path of a photo-electric conversion section of a camera tube, and more particularly to an improvement of such a camera apparatus whereby phase errors of a color signal resulting from variations in viewed light intensity can be substantially reduced.
The present application is related to the copending commonly assigned application Ser. No. 784,867, filed Oct. 4, 1985 now U.S. Pat. No. 4,736,242.
The single-tube type of color video camera, utilizing a stripe filter for color separation, is now in widespread use. With such a camera, light from a scene being viewed by the camera is passed through the stripe filter to a photoconductive layer of a photelectric conversion section, which is raster-scanned by an electron beam. As the electron beam passes across each portion of the photoconductive layer corresponding to a specific color of filter stripe, i.e. illuminated by light transmitted through that stripe, the charge which has become stored on that photoconductive layer portion as a result of incident light is discharged, whereby a current flow occurs. The level of this current represents the light intensity of the corresponding portion of the viewed scene, while the timing at which the current flow occurs (i.e. during a horizontal scanning interval) indicates the color of light represented by this current. An output current signal is thereby produced from the camera picture tube which includes a color multiplex carrier signal component.
Ideally, the respective timings at which discharge current flows begin, for portions of the photoconductive layer corresponding to different color stripes, should be independent of the intensity of light which is viewed by the camera. However with a prior art single-tube color video camera this is not the case. Specifically, if the beam current of the scanning electron beam is fixed, then the time required to discharge a portion of the photoconductive layer (i.e. lying below a specific stripe of the filter) that is illuminated with relatively high intensity of light will be significantly longer than the time required to discharge a portion illuminated by light of low intensity. As a result, the phase of the color multiplex carrier signal produced by the camera will vary in accordance with variations in the level of light which is transferred through the color stripes. Since the operation of such a camera apparatus is based upon the assumption of a fixed relationship between successive electron beam scanning positions and the timings of color carrier signal portions corresponding to respective color stripes, such phase deviations make it impossible to obtain an accurate color video signal under conditions of varying light intensity in the scenes viewed by the camera.